Adaptive Traits in Desert Ungulates Under Thermal Stress
Keywords:
adaptive traits, dehydration, heat shock protein, infrared thermography, biologger, climate change, Gazella, dromedary camel, Arabian oryx, HSP70, body temperature, heterothermy, thermoregulation, desert ungulatesAbstract
Desert ungulates inhabiting the hyperarid zones of the Arabian Peninsula, Sahara, and Central Asian deserts face
extreme thermal environments characterised by ambient temperatures exceeding 45degC, solar radiation loads of
800-1,000 W/m2, and chronic water restriction, yet maintain core body temperatures within physiologically tolerable limits
through a suite of morphological, physiological, and behavioural thermoregulatory adaptations that are among the most
extreme documented in terrestrial mammals. This study quantified adaptive thermoregulatory traits in four desert
ungulate species -- Arabian oryx (Oryx leucoryx), dromedary camel (Camelus dromedarius), dorcas gazelle (Gazella
dorcas), and sand gazelle (Gazella subgutturosa) -- using implanted biologgers recording core body temperature (T(b))
at 15-minute intervals (n = 84 individuals; 6-24 months per individual), combined with GPS-linked ambient temperature
sensors, infrared thermography of surface temperature distribution, and haematological sampling for heat shock protein
(HSP70) and osmolality indicators of hydration status. Core body temperature heterothermy amplitude (T(b) range over
24 hours) ranged from 2.8 +- 0.4degC (dorcas gazelle; low heterothermy) to 6.4 +- 0.8degC (dromedary camel; extreme
heterothermy). T(b) was significantly correlated with ambient temperature (r = +0.84, p < 0.001) and hydration status (r =
-0.72, p < 0.001). HSP70 expression (plasma concentration ng/mL) was significantly elevated in dehydrated individuals
across all four species (dehydrated: 48.4 +- 12.4 vs. hydrated: 18.4 +- 6.4 ng/mL; t = 8.42, p < 0.001). Behavioural
thermoregulation (shade-seeking, activity restriction) reduced T(b) by 1.2-2.8degC relative to predicted T(b) without
behavioural adjustment. Climate projections under SSP5-8.5 by 2070 indicate mean ambient temperature increases of
3.8-4.2degC in the study areas, which when applied to the T(b)-ambient temperature regression functions predict that all
four species will experience T(b) exceeding their documented thermal tolerance limits (40.5-42.0degC) for significantly
longer daily periods, identifying behavioural thermoregulation capacity as the key trait determining climate change vulnerability in desert ungulate populations.
